1. Field of the Invention
The present invention relates to a focal-plane shutter for a digital still camera.
2. Description of the Related Art
As an example of focal-plane shutters for digital still cameras, an arrangement is known wherein a space between a shutter base plate and an auxiliary base plate is partitioned into two blade rooms, two shutter blades, which are referred to a first blade and a second blade, are disposed in these blade rooms, respectively, and exposure is continuously performed on an imaging face in the shape of a rectangle through a slit formed by these shutter blades at the time of taking a picture. Furthermore, examples of digital still cameras include an arrangement having only an optical finder, an arrangement having only an electronic finder (using a monitor as a finder), and an arrangement having both. Accordingly, the aforementioned focal-plane shutters can be classified into normally-open types and normally-closed types depending upon the difference of action, with different configurations being employed according to the difference in the type of the shutter.
On the other hand, as a focal-plane shutter for a digital still camera, an arrangement is known wherein one blade room is formed between the shutter base plate and the auxiliary base plate, and one shutter blade is disposed in the blade room. Examples of the above-described shutter include an arrangement wherein following the end of exposure for photography, the photography optical path is simply temporarily closed by the shutter blade, and an arrangement wherein the exposure time period for photography is ended by the closing action of the shutter blade. In either case, the focal-plane shutters can be classified into normally-open types and normally-closed types, with different configurations being employed according to the difference in the type of the shutter.
Furthermore, each shutter blade has essentially the same configuration regardless of whether a focal-plane shutter including two shutter blades or a focal-plane shutter including only one shutter blade. The focal-plane shutter comprises multiple arms mounted on the shutter base plate and one or more blades supported by these arms. In the event that the arms are reciprocally rotated in a predetermined range of angle, the blades are moved between the position where the photography optical path is closed by the blades and the position retracted from the optical path.
There is the need to employ a focal-plane shutter having a configuration corresponding to whether the normally-closed method or the normally-open method, regardless of whether the focal-plane shutter including two shutter blades and the focal-plane shutter including only one shutter blades. This restriction is by no means preferable from the point of development of the camera and manufacturing of the shutter. Accordingly, development of a focal-plane shutter which can be employed in both cameras employing the normally-open method and cameras employing the normally-closed method with the same shutter configuration is desired. Furthermore, development of such a focal-plane shutter is desired since that would allow for a camera to be developed wherein the user can take a picture with the normally-open method and the normally-closed method being selected.
The present invention has been made to solve the above-described problems, and accordingly it is an object thereof to provide a focal-plane shutter for a digital still camera for taking a picture both with the normally-open method and the normally-closed method, with the same configuration.
In order to achieve the above objects, a focal-plane shutter for a digital still camera according to the present invention comprises a first base plate having a first aperture for a photography optical path; a second base plate, having a second aperture for a photography optical path which matches the first aperture, for forming a blade room between the first base plate and the second base plate; a plurality of arms mounted on one of the first and second base plates; a shutter blade made up of one or more blades, supported by the plurality of arms, which is reciprocally moved between a first position where the shutter blade is retracted from the photography optical path and a second position where the shutter blade covers the photography optical path in the blade room; a driving member, mounted on the first base plate outside the blade room, which presses one of the arms only at the time of action by the force from a driving spring so that the shutter blade is moved in a first direction; a motor, mounted on the second base plate outside the blade room, which moves the shutter blade in the first direction and in a second direction, through one of the plurality of arms corresponding to reciprocal rotation of the stator of the motor; a set member, mounted on the first base plate outside the blade room, which moves from an initial position so that the driving member is moved to a set position against the force from the driving spring; and holding means which hold the driving member at a set position at least during movement of the set member for returning to a set position, with the holding force thereof being released during the movement of the shutter blade by the force from the driving spring. In this case, an arrangement may be made wherein the arm operated by the driving member and the arm operated by the motor is the same arm, whereby a preferable configuration is obtained.
With the focal-plane shutter for a digital still camera according to the present invention, a current may be continuously applied to the motor so that the shutter blade is forced so as to move in the second direction from the point in time at which the movement of the shutter blade in the second direction is started, up to the point in time at which the shutter blade reaches a second position following which a predetermined time period elapses, thereby preventing the shutter blade from bounding at the second position. Furthermore, the current may be continuously applied to the motor from the point in time at which the movement of the shutter blade in the first direction is started up to the point in time immediately before the shutter blade reaching the first position, obtaining stable movement of the shutter blade in the first direction.
Furthermore, with the focal-plane shutter for a digital still camera according to the present invention, a current may be applied to the motor so that the shutter blade is forced so as to move in the first direction, from the point in time at which the movement of the shutter blade in the first direction is started, at least up to the point in time at which the shutter blade is stopped at the first position by coming into contact with a stopper, thereby preventing the shutter blade from bounding at the first position.
Furthermore, the focal-plane shutter for a digital still camera according to the present invention may further comprise: an intermediate plate, having a third aperture which matches the first and second apertures for the photography optical path, which partitions a space between the first base plate and the second base plate into two blade rooms so that the shutter blade is disposed in one of the two blade rooms; a second shutter blade, made up of one or more blades and supported by a plurality of arms mounted on one of the two base plates, which is reciprocally moved between a first position where the shutter blade covers the photography optical path and a second position where the shutter blade is retracted from the photography optical path in the other blade room of the two blade rooms; a second driving member, mounted on the first base plate outside the blade room, which moves the second shutter blade in a first direction at the time of being moved by the force from a second driving spring, and moves the second shutter blade in a second direction at the time of being moved to a set position by the set member against the force from the second driving spring; and second holding means which hold the second driving member at a set position at least during movement of the set member for returning to the initial position, with the holding force thereof being released during the movement of the second shutter blade by the force from the second driving spring.
According to the present invention, the first shutter blade may be a front blade, and the second shutter blade may be a rear blade.
With the present invention, shutter action can be performed with both the normally-open method and the normally-closed method, with the same configuration, regardless of whether a focal-plane shutter including two shutter blades or a focal-plane shutter including only one shutter blade. This advantage is preferable from the point of development of the camera and manufacturing of the shutter, and furthermore would allows for a camera to be developed wherein the user can take a picture with the normally-open method and the normally-closed method being selected.